This application is to survey nursing patterns, activity, and onset of menses in an indigenous community in Argentina. It is thought that more intense nursing (more frequent and longer duration) prevents ovulation. The investigators hypothesize that, along with nursing intensity, positive energy balance (high nourishment/low workload) is inversely related to lactational infertility. Also, maternal age is postulated to have a U-shaped relationship with on lactational infertility. The investigators are interested in studying this hypothesis in Toba women of Argentina because they have, in general, intense nursing patterns, positive energy balance (high body mass index and low workloads, and short periods of lactational amenorrhea. The study would select 100 lactating women between ages 14 and 45 with infants between 0 to 12 months of age. Monthly interviews would be conducted to collect data on both infant=s and mother=s diet and activities. A subsample of 60 women would be selected for monthly home visits when four hour observation sessions would take place. Amenorrhea by maternal report would serve as an indicator of lactational infertility. Data collection would occur over a 14 month period, but funds are sought for 8 months of that, plus 16 months of data analysis support.